Question for H & G Electricians re: generator wiring

I have a question regarding wiring a 30amp box to connect a portable generator to my house via a 30amp cord. I had electrician wire a 30 amp (four prong L14-30) power inlet box into my service panel. The way its set up, I turn main breaker off and service goes into subpanel B, and I can turn on select individual breakers to power lights, ceiling fans, window unit AC’s, etc.. Everything works fine on my older Briggs & Stratton 5000 watt generator. However, I just bought a new Champion 9200 watt generator and when I plug it in nothing happens. I checked power output from new Champion generator with a multimeter and its generating power. Could the power inlet box be wired improperly? Is it possible that the two hot wires (line one and two) are backwards? Would that matter? To further the issue, I also had a Honda 5000w generator that a neighbor gave me that I tried to plug in with the same 30 amp cord, and every time I connected it, it would automatically trip the breaker on the generator. Both Honda generator and 30 amp cord were tested at the dealership and everything was fine. I am out of town for a few days, and plan to call the electrician to come and check things out, but was curious as to what the issue might be? Thoughts?